It is often desirable to coat an article, substrate or film in order to modify the properties. A particularly desirable coating is that of an elastic film, i.e., a film which is capable of being stretched without breaking and returning to substantially the same form. In this manner, the article, substrate or film can be used to form structures requiring elasticity.
Elastic films made from elastomeric polymers have found use in laminates. Laminates are conveniently made by coating a substrate, for example, paper or film, with an elastic layer by extrusion coating. Extrusion coating is a process whereby a polymer or blend of polymers is fed into an extruder hopper. In the hopper the polymer or blend is melted and passed through a die to form a web. The web is then extruded onto the substrate through a nip roll/chill roll interface, for example, so that the molten web is pressed onto the substrate. The substrate is cooled by the chill roll and the wound up at a winder.
Elastic films made from elastomeric polymers have found particular use in laminates wherein the substrate is a nonwoven fabric because the elastic film imparts elasticity to the nonwoven laminates. Such elastic nonwoven laminate materials have found use in the hygiene and medical market particularly in such applications as elastic diaper tabs, side panels of training pants, leg gathers, feminine hygiene articles, swim pants, incontinent wear, veterinary products, bandages, items of health care such as surgeon's gowns, surgical drapes, sterilization wrap, wipes, and the like. These materials may also find use in other nonwoven applications including but are not limited to filters (gas and liquid), automotive and marine protective covers, home furnishing such as bedding, carpet underpaddings, wall coverings, floor coverings, window shades, scrims etc. These elastic films can be incorporated into laminate designs such as those described in WO9003464A2 and U.S. Pat. Nos. 4,116,892 and 5,156,793.
Many different processes are often employed to make single or multi-layer elastic films. Such processes can include bubble extrusion and biaxial orientation processes, as well as, tenter frame techniques. In order to facilitate elasticity, the elastic film is usually employed singly or as the outermost layer in the case of multi-layer films.
Elastic films are often prepared using cast film processes. In a typical cast film process the molten polymer is extruded through a die and then the molten film is drawn to the nip/chill rolls where it is rapidly cooled on the chill roll. Particularly as the speed of the production increases, a phenomenon known as draw resonance can occur under particular extrusion conditions especially when a nip is used. Draw resonance is the name given to periodic fluctuations in the thickness of the film in the machine direction (MD) which corresponds to periodic variations in the film width in the cross direction (CD). Draw resonance results in film instability which can restrict the productivity of commercial processes. Draw resonance is known to be a particular problem for polyolefin elastomers, particularly linear polyolefins. Accordingly, it is a goal to reduce or eliminate draw resonance in the production of films, particularly in the production of elastic films. This phenomenon has been described previously in the scientific literature. The following are some examples:    Silagy, D, J. Non-Newtonian Fluid Mech., “Stationary and Stability Analysis of the Film Casting Process”, page 563-583, vol. 79 (1998).    Silagy, D., “A Theoretical & Experimental Analysis of Line Speed Limitations in the Film Casting of Polyethylene”, 6th European TAPPI Seminar on Polymers, Films, and Coatings, Copenhagen, Jun. 8-9, 1999.    Denn, M, “Instabilities in Polymer Processing”, AICHE J., (22), No. 2, p 209-236, (March, 1976).    Anturkar, N., “Draw Resonance Film Casting of Viscoelastic Fluids: a Linear Stability Analysis”, J. of Non-Newtonian Fluid Mech., 28, p 287-307, (1998).    Pis-Lopez, M., Multilayer Film Casting of Modified Giesekus Fluids Part 1. Steady State analysis”, J. Non-Newtonian Fluid Mech., 66 p 71-93, (1996).    Bortner, M., “Dependence of Draw Resonance on Extensional Rheological Properties of LLDPE”, SPE 2003 ANTEC.     Smith, Spencer, “Numerical Simulation of Film Casting Using an Updated Lagrangian Finite Element Algorithm”, Polymer Engineering and Science, May 2003, Vol. 43, No. 5, page 1105.
Elastic films made with conventional polyolefin elastomer or plastomer compositions in an extrusion lamination/coating application are often slow or difficult to produce due to draw resonance and neck-in. Accordingly, compositions that are suitable for elastic films and laminates that can be produced more easily and have the same or better elasticity are desired.
Examples of processes, manufacture, and articles suitable for use with the current inventions include, but are not limited to, EP472942B1, EP0707106B1, U.S. Pat. No. 4,422,892, U.S. Pat. No. 4,525,407, U.S. Pat. No. 4,720,415, U.S. Pat. No. 4,965,122, U.S. Pat. No. 4,981,747, U.S. Pat. No. 5,114,781, U.S. Pat. No. 5,116,662, U.S. Pat. No. 5,169,706, U.S. Pat. No. 5,226,992, U.S. Pat. No. 5,336,545, U.S. Pat. No. 5,514,470, WO9003258A1, WO9003464A2, EP0575509B1, U.S. Pat. No. 6,605,172, U.S. Pat. No. 5,650,214, U.S. Pat. No. 3,833,973, U.S. Pat. No. 3,860,003, U.S. Pat. No. 4,116,892, U.S. Pat. No. 5,151,092, U.S. Pat. No. 5,156,793, U.S. Pat. No. 5,691,035, U.S. Pat. No. 5,891,544, U.S. Pat. No. 5,916,663, U.S. Pat. No. 6,027,483.
Advantageously, the compositions of the present invention are suitable for elastic films and laminates. Elastic films and laminates can be readily produced from the inventive compositions and often have the same or better elasticity than conventional compositions. The compositions suitable for use in elastic films and laminates comprise at least one ethylene/α-olefin interpolymer, wherein the ethylene/α-olefin interpolymer:                (a) has a Mw/Mn from about 1.7 to about 3.5, at least one melting point, Tm, in degrees Celsius, and a density, d, in grams/cubic centimeter, wherein the numerical values of 30 Tm and d correspond to the relationship:Tm≧858.91−1825.3(d)+1112.8(d)2; or        (b) has a Mw/Mn from about 1.7 to about 3.5, and is characterized by a heat of fusion, ΔH in J/g, and a delta quantity, ΔT, in degrees Celsius defined as the temperature difference between the tallest DSC peak and the tallest CRYSTAF peak, wherein the numerical values of ΔT and ΔH have the following relationships:ΔT>−0.1299(ΔH)+62.81 for ΔH greater than zero and up to 130 J/g,ΔT>48° C. for ΔH greater than 130 J/g,        
wherein the CRYSTAF peak is determined using at least 5 percent of the cumulative polymer, and if less than 5 percent of the polymer has an identifiable CRYSTAF peak, then the CRYSTAF temperature is 30° C.; or                (c) is characterized by an elastic recovery, Re, in percent at 300 percent strain and 1 cycle measured with a compression-molded film of the ethylene/α-olefin interpolymer, and has a density, d, in grams/cubic centimeter, wherein the numerical values of Re and d satisfy the following relationship when ethylene/α-olefin interpolymer is substantially free of a cross-linked phase:Re>11481−1629(d); or        (d) has a molecular fraction which elutes between 40° C. and 130° C. when fractionated using TREF, characterized in that the fraction has a molar comonomer content of at least 5 percent higher than that of a comparable random ethylene interpolymer fraction eluting between the same temperatures, wherein said comparable random ethylene interpolymer has the same comonomer(s) and has a melt index, density, and molar comonomer content (based on the whole polymer) within 10 percent of that of the ethylene/α-olefin interpolymer; or        (e) has a storage modulus at 25° C., G′(25° C.), and a storage modulus at 100° C., G′(100° C.), wherein the ratio of G′(25° C.) to G′(100° C.) is in the range of about 1:1 to about 9:1        
wherein the ethylene/α-olefin interpolymer has a density of from about 0.85 to about 0.89 g/cc and a melt index (I2) of from about 0.5 g/10 min. to about 20 g/10 min.